IS THE ORGANISM A MECHANISM? 66 1 



that by which they are brought about in the organism. Of 

 themselves they do not occur free in inorganic nature ; they 

 occur only as the result of direction conferred on physico-chemical 

 reactions by the intelligence of the experimentalist — that is, 

 by life. 



The organism therefore exhibits tendency which is opposed to 

 the direction taken by inorganic processes. But the latter is, as 

 we have seen by considering Boltzmann's example of a physically 

 changing gas, not necessarily always the same. It is highly 

 probable that any physical change whatever will proceed as the 

 second law of thermodynamics indicates, that is, in such a way 

 that entropy will be augmented. But it may proceed otherwise : 

 two gases at different temperatures, and in thermal contact with 

 each other, will most probably mix so that in a short time the 

 temperature of the mixture will everywhere be the same. The 

 change is irreversible, we say, in the sense that it is highly 

 improbable that it will reverse of itself; but it may reverse, and 

 there are regions in the whole mass of gas where the temperature 

 is higher than in adjacent regions. Yet the probability of a 

 reversible change is infinitesimally small, and the dimensions of 

 the regions in which the temperature departs from uniformity 

 are also infinitesimally small. 



The universe which is physically active is, both in its 

 dimensions and its duration, very great. But the material 

 universe that we know occupies only an infinitesimally small 

 part of space : probably the stars that we know, that is, those 

 which radiate light are only a small fraction of the whole material 

 universe. To say this is the same thing as to say that it is 

 highly improbable that any part of the entire universe is 

 physically active — has been the theatre of a restoration of 

 available energy, or a reversal in sign of the second law of 

 thermodynamics. But life also is highly improbable. The total 

 mass of organised substance on our earth is infinitesimally small 

 in comparison with the mass of the globe. The mass of nitrogen 

 in the chemically combined form is an infinitesimally small part 

 of the total nitrogen of the atmosphere. Vegetation, rich as it 

 may be on some parts of the earth, is entirely absent over other 

 large areas, and is anywhere only a film of almost inconceivable 

 tenuity in comparison with the bulk of the planet. If living 

 substance is the expression of a reversal in sign of the second 

 law of energetics, its probability of occurrence is of much the 



